Amazon have restricted an item that is not in the restricted list

I have a product that has been selling on Amazon for several years without issue. We have 2 variations of this product. One variation has suddenly been marked as “Inactive” in my inventory. When I go to resolve it, it says I need to apply to sell this product since it is restricted. It then says Amazon is not accepting applications at this time.

I’ve spoken to several representatives by phone, email and by chat, and they keep saying that we simply have to apply for approval, and since we can’t apply for approval, then there’s nothing they can do. I’m the brand owner of the product, so I know it’s not a brand-related issue.

Since I know the product is not part of the restricted list (since both myself and many other sellers sell this type of item on Amazon), what else can I do to get the listing active and product sellable again?

Thanks